What is a wired OR?

Question:

What is a wired OR?

Answer:

To detect a change in two or more signals, an OR gate is usually used. Wired OR is a technique to reduce the number of gates and to use only one signal.
In practical terms, a negative logic circuit is effective.

If the output signals of the ordinary bipolar circuit and MOS are combined into one, short-circuiting occurs if one of the signals is inverted.
By contrast, however, the output of an open collector (bipolar) or open drain (MOS) can take a logical sum (negative logic) by connecting one pull-up resistor because there is no short path to the power supply.
In this case, it must be assumed that the resistance is driven at a low level of the worst case, so that only one signal becomes active.